"It's amazing to think that a satellite that was designed in the mid-1970's and built in the early 1980's is still operating perfectly in 2007!"

It's not very great achievement, Ulysses at last was launched in 1990. Pioneer 6, the first in a series of solar-orbiting satellites was launched December 16, 1965. Although the spacecraft have not been regularly tracked for science data return in recent years, a successful telemetry contact with Pioneer 6 was made on December 8, 2000 to celebrate 35 years of continuous operation since launch. As of March 15, 2006, Pioneer 6 is still described as "extant", and is the oldest operating space probe (if still operating).

Back when I was in university, a dozen of years ago I played with simulating Ulysses' orbit. In that occasion I "discovered" the second flyby of 2003.Ulysses crosses Jupiter's orbit every 6.5 years, and approaches it every 13 years, but IIRC, the encounter distance is increasing and there will be no more flybys during all of the 21st century.

I explored Ulysses orbit evolution with JPL HORIZONS system. Here are some interesting encounters till the end of XXI century:

November 7, 2098 Ulysses will be kicked out of the Solar system by Jupiter's gravity. Spacecraft's final trajectory will be highly hyperbolic (eccentricity~1.42), so it will be travelling very fast and one day, thousands years from now, Ulysses will reach some star.

Looks like my old thread was just a few years too early! I'm not criticizing the decision to switch off the HGA but I want to understand exactly what happened. They switched off the 60W HGA in attempt to divert the extra energy to the heater and science instruments instead but found that not only would the HGA not turn back on again but they couldn't even re-route the power to the heaters either. Right? But is the fuel freezing faster than expected now due to the fact that those 60W which would have been dissipated in the HGA subsystem are wasted out the RTG?

Remember that Ulysses needs to periodically re-orient it's high-gain antenna to point toward Earth. Though it's now irrelevant, the X-band beam is several times narrower than the S-band beam due to the diffraction limit of the dish antenna. We're moving out of the S-band beam, I presume, and data rates will drop to useless levels. There may be an omni antenna (I'd presume there is) for tracking immediately post-launch, but data rates would be like the raw data rate (before heroic efforts) of Galileo at Jupiter or worse, and depending on spacecraft orientation, might drop to zero for months or years. The spacecraft might well continue to transmit for some more years, but it's mission is essentially about to end.

Remember that Ulysses needs to periodically re-orient it's high-gain antenna to point toward Earth. Though it's now irrelevant, the X-band beam is several times narrower than the S-band beam due to the diffraction limit of the dish antenna. We're moving out of the S-band beam, I presume, and data rates will drop to useless levels.

Certainly once the s/c loses attitude control the mission is essentially over.The S-band and X-band both go through the high-gain antenna, but the S-band output power is only 5 watts compared to 20 on X-band, so the maximum data rate is pretty limited (I believe 128 bps compared to 1024 bps on X-band through DSN 34m).

Presumably, if they didn't have the power problem as well, they'd keep the mission going on S-band.

It's not very great achievement, Ulysses at last was launched in 1990. Pioneer 6, the first in a series of solar-orbiting satellites was launched December 16, 1965. Although the spacecraft have not been regularly tracked for science data return in recent years, a successful telemetry contact with Pioneer 6 was made on December 8, 2000 to celebrate 35 years of continuous operation since launch. As of March 15, 2006, Pioneer 6 is still described as "extant", and is the oldest operating space probe (if still operating).

Pioneer 6 is an incredibly simple spacecraft, operating in a relatively consistent thermal environment. Ulysses is far more complex and relies on a finite power source. The fact that it lasted all these years and is only now being killed by the natural decay of RTGs (or the side effects from that lack of power) is very remarkable. Plus, Ulysses could have been preserved longer if they elected to turn the instruments off, but what would be the point in that?

Fuel-bearing components are specified to be kept above 5°C. This is to prevent the fuel, hydrazine, from freezing, which would cause two problems. Firstly, the fuel would not flow to the thrusters and no manoeuvres would be possible. Secondly, if the fuel were to subsequently thaw, pockets of expanding liquid could form possibly rupturing RCS sections.

During the prime mission (1990-1995), meeting this requirement was not difficult, but with RTG power levels becoming so low it is no longer possible to keep remote RCS components above (5+margin)°C, particularly when the margins have been made particularly generous. In order to keep as much of the payload operating as safely possible, it is necessary to trim thermal margins to the lowest level. This in turn necessitates careful calibration of the spacecraft Thermal Model against in-flight temperature data.

The Reaction Control Subsystem (RCS) has several thermistors that measure component temperatures directly, shown on the right. There are also thermistors elsewhere on the spacecraft that can be used to infer RCS component temperatures.

Early in the mission, the available telemetry and generous thermal margins were sufficient to ensure compliance, however with steadily decreasing power availability, greater scrutiny of margins and more insight on the thermal behavior of all RCS components was necessary.

- - -

Sounds as if since 1995 things have been dicey when themal heating was low... Hydrazine freezes at 34 F (4 C) so holding temps above 5 C is a minimum requirement.

I know that during the Jupiter Distant Encounter in February of 2004, Ulysses had to turn its tape recorder off to run all of its instruments at once. However, during the ~40 days around the encounter, it had round-the-clock DSN coverage, so it had little effect. Once Ulysses began approaching the sun again, it was able to turn its heaters off, freeing up power.

November 7, 2098 Ulysses will be kicked out of the Solar system by Jupiter's gravity. Spacecraft's final trajectory will be highly hyperbolic (eccentricity~1.42), so it will be travelling very fast and one day, thousands years from now, Ulysses will reach some star.

I'm wondering how accurate HORIZONS data can possibly be for such distant dates. There has to be a number of unmodelled factors affecting orbital evolution of the spacecraft that the system doesn't take into account such as solar radiation pressure, slow outgassing from the spacecraft, etc. These will, given enough time, measurably perturb the orbit and I'm wondering what the real flyby distance and slingshot effect will be in 2098. Even tiny perturbations now can lead to large deviations in the future predicted passes.

I wouldn't put my hand into the fire and say Ulysses is heading out of the solar system, let alone heading out on a highly hyperbolic trajectory. Move the closest approach point to Jupiter by a million km in one direction and it could end up being decelerated by Jupiter instead.

EDIT: To give a sense of what I'm talking about, consider Jupiter's orbital velocity is 13 km/s and so it needs some 21 hours to cross a million kilometers. If Ulysses is early in its orbit by a mere 20 hours at the time of the 2098 flyby, the outcome could be radically different. A 20 hour cumulative in 90 years is really not much, especially since weak forces like light pressure tend to not change orbits much, but change their circumference a bit, which then brings timing differences that accumulate over time.

For most of that time it should be away from major influences. However, when I run the numbers, I am seeing a Jupiter flyby in 2092 that is fairly close and would extend the orbit too far out to be thrown out of the solar system in 2098. In fact, at least on the "kiloyear" level, the orbit looks stable.

Yep, I made a stupid mistake. Or even two. As for the solar light pressure, that's significant pertubator indeed. When I entered actual Ulysses area-to-mass ratio and size into the HORIZONS, results were changed dramatically. For example, Jupiter-2098 encounter:

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